Research in the Wamser Group
at Portland State University

Interfacial Polymerization

Two different monomers react at an interface

Thin films of polymeric porphyrins are created by the technique of interfacial polymerization. Two reactive porphyrin monomers are dissolved separately in immiscible liquids; rapid reaction occurs only at the interface between these two solutions, creating a thin polymer film. In the case of acid chloride and amine derivatives, a polyamide film is created. As the polymerization reaction proceeds, the interfacial film becomes a barrier that slows further reaction; hence interfacial polymer films can be exquisitely thin (10 - 100 nm). Nevertheless, these films absorb visible light well and undergo photoinduced charge transfer reactions that are directional, analogous to the charge transport membranes of natural photosynthesis. The directionality of these films is caused by an asymmetry of functional groups on the porphyrin units within the polymer film; specifically, excess amine groups appear on the surface of the film that was made in contact with the porphyrin amine derivative and excess carboxylic acid groups appear on the surface of the film that was made in contact with the porphyrin acid chloride derivative (acid chlorides are hydrolyzed to carboxylic acids during the workup of the finished film). This structural asymmetry of the thin films is a novel feature that is still under study both experimentally and theoretically. The structural asymmetry leads to the photochemical asymmetry because the redox potentials of the different porphyrins are such that electron transfer is favored from aminoporphyrins to carboxy-porphyrins.

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